RE: Solenoid Radiator valves

["Kevin Hawkins" <lists@xxxxxxx>]

I have been meaning to have a go at this (modulating the boiler directly) =
=96 currently I have a modulating condensing boiler feeding about 8 zones =
=96 some of which are single rooms =96 I did this where there were more
tha=
n one radiator in a room =96 and particularly where they were the old cast
=
iron ones =96 having previously cracked a radiator fitting new valves.

I went originally with the recommended controller which is both=
fancy and dumb !  It runs on a single pair of wires to the boiler and prov=
ides full monitoring and display of all the various temps, boiler, flow,
re=
turn, room, hot water, outside etc =96 however it can=92t program HW
separa=
te from heating and has no facilities like advance for 1 hour or anything.
=
The big problem though is it modulates to create a flow temperature to
main=
tain the temp in the room it sits in =96 so I have had to mount it in the
h=
all =96 the coldest room. It is supposed to compensate such that the room
a=
lways reaches the setpoint at exactly the same time each day =96
effectivel=
y coming on earlier if it is cold outside or the room needs extra heating.
=
Now , caused by my meddling it fails to do this.

My problem was  that once that room is satisfied the water circulation
drop=
s in temp and so if other rooms need extra heat they can=92t get it. I
sort=
of worked around this by setting the desired temp very high in the hall =
=96 and then also reducing the flow through the radiators there to cause
it=
great difficulties in becoming satisfied but the nett effect was that the =
boiler is confused I think with the heating characteristics of that room
an=
d knows that it can=92t heat it predictably so it ambles along at a mid
tem=
perature =96 this has allowed other rooms to become satisfy when needed
but=
has negated the whole advantages of fhe modulating approach =96 I need to =
rethink it all =96 either by a manual approach or by using a multi sensor
a=
rrangement across the house =96 unfortunately I know little about this and
=
although I have asked Potterton (commercial) for help the two different
com=
panies they recommended were not very conversant with the solutions =96
one=
volunteering a =A35K buildings management package and one saying they didn=
=92t know.

The fortunate thing is that I can modulate my boiler with 0-10V and so =
I think I may have a go myself. I am told it is a science getting the
respo=
nse curves right and I have never really understood why the external
temper=
ature is so vital =96 I would have thought that you would just calculate
th=
at to raise a room from say 13 to 22 degrees takes 20 minutes =96 I can
see=
that the outside temp has some effect on this =96 if it is cold outside it=
will take longer than if it is warm but is that the only effect > ?
effect=
ively the heat loss caused by the differential ? I am also a little loathe
=
to override the boilers control of all these sensors, flow return ,
outside=
, room etc as it is supposedly a clever piece of kit =96 it has
=91European=
House style models=92 built in =96 but I can=92t find a reasonable cost wa=
y of expanding it=92s operation from single room sensing to muti room.

=20

BTW =96 If anyone with  a commercial interest / expertise in  this would
li=
ke to talk to me I would welcome it =96 I am very willing to buy in a
reaso=
nable cost solution. It is a Potterton EuroCondense 65 boiler.

=20

Kevin

=20

-----Original Message-----
From: Neil Ball [mailto:neilball@xxxxxxx]=20
Sent: 07 April 2003 15:49
To: ukha_d@xxxxxxx
Subject: RE: [ukha_d] Solenoid Radiator valves

=20

I can see the problem now Kevin - as you say, most valves do not give
balan=
ced flow across their opening range, most have almost 100% flow as soon as
=
they are partially opened which gives very little controllability.

Just another thought, are you measuring room temperature with sensors? If
s=
o, have you considered controlling the boiler output based on heating
deman=
d (direct boiler compensation)? Most commercial systems use either outside
=
weather compensation control, heating demand compensation based on room
sen=
sors, or a combination. Here you reduce the effects of the poor valve
autho=
rity as instead of only allowing a very small amount of high temperature
wa=
ter into the radiator you allow much more at a reduced temperature thereby
=
increasing the overall level of control. Works very well with condensing
bo=
ilers as it maximises the time the boiler is in full condensing mode for
mu=
ch of the heating season. You'll need to add at least on pipe sensor and
us=
e the heating demand to calculate the required boiler flow temperature,
and=
control the boiler temperature through simple on/off switching. You might =
also have to add a hot water sensor to make this a zone so that can
influen=
ce this calculation as well and boost the boiler temperature when the
cylin=
der needs heating.

With regard to positioning raise/lower valves then it is not too hard -
you=
simply roughly position the valve based on room heating demand, and then p=
ulse the valve in small increments thereafter based on room response. As
lo=
ng as you measure the full stroke time of the valve it becomes a
time-based=
operation, and you can always use the full stroke time plus a margin whene=
ver the valve is moved fully open or closed to ensure it gets registered
to=
the extreme of it's travel. In reality you get pretty good positioning wit=
hout the expense of 0-10v control (bear in mind that most 0-10v actuators
s=
imply turn this signal back into a raise/lower signal internally to drive
t=
he motor anyway).

Let me know how you get on.

Neil.




-----Original Message-----
From: Kevin Hawkins [mailto:lists@xxxxxxx]=20
Sent: Monday, April 07, 2003 13:58
To: ukha_d@xxxxxxx
Subject: RE: [ukha_d] Solenoid Radiator valves


I have played quite a bit with the algorithms for the ON OFF control =96
wh=
ich I have in about 4 rooms here. My problem comes because of the heat
rete=
ntion in the radiators. They are the very old fashioned cast iron ones.
Now=
as soon as the valve is opened they heat up very quickly (as the water flo=
wing past is already very hot) but they hold heat for a long time, causing
=
the overshoot =96 so I am faced with almost pulsing the valves open for a
v=
ery short time to only heat the radiator up a little. I even played with a
=
temp sensor attached to the radiator. Unfortunately this then also gets
com=
plicated by the flow temp at the valve and the flow rate or pressure =96
bo=
th these being effected by other demands from TVR=92s and zones. In one of
=
the rooms the radiators are more modern meaning they are far more
efficient=
at radiating heat and hence cool much faster =96 this room I have managed =
to cater for the hysteresis far better with an algorithm.=20

TBH I had intended all my valves to be proportional type 1 or raise/lower
t=
ype 2 below, but I had installed the traditional zone valves assuming I
cou=
ld just exchange the actuators at a later time for proportional ones =96
bu=
t you can=92t get proportional or raise/lower exchange actuators for
standa=
rd zone valves =96 so I had to work around or fit new valves as well.

Neil =96 when I said proportional I meant to include raise/lower =
in that category =96 I think we are talking about three types here
aren=92t=
we ??

1)       The type that is either fully open or fully closed (but takes a
fe=
w secs to move from one to the other)

2)       The type that you apply say 0-10V to and they are proportional ie
=
3V is 30% open

3)       The raise lower type =96 you drive them with a succession of
pulse=
s to move them from one position to the next ( or maybe even a timed
voltag=
e application) =96 then they stay wherever they are left =96 if you drive
t=
hem 2/3 open then that is where they stay. These take a little tracking
and=
have to be calibrated against end positions periodically =96 I think these=
are the lowest cost of the 2 and 3 and what I will probably end up using.

There is a fourth type which is what most of my radiators use at the
moment=
=96 it is a sort of =91bodged=92 TVR. Basically I have TVR=92s with a capi=
llary and remote sensor mounted in a small plastic box. You set the
require=
d temperature on the standard mechanical rotary TRV. However also mounted
i=
n the little sensor box is a small electric element that applies heat to
th=
e sensor in proportion to the voltage applied to it. Hence you can set
back=
that room by 2 degrees by applying 2V or by 5 degrees by 5V etc. This work=
s very well to regulate the room as the control is effectively truly
propor=
tional =96 you can also effectively turn a  room ON or OFF this way. I am
n=
ot sure these are manufactured anymore =96 they were made by Danfoss.



I am really interested in this subject as I have yet to implement most of
m=
y control here =96 so please do keep us updated on anything you find=85



Kevin





-----Original Message-----
From: Dave McLaughlin [mailto:dave@xxxxxxx]=20
Sent: 07 April 2003 12:36
To: ukha_d@xxxxxxx
Subject: RE: [ukha_d] Solenoid Radiator valves



Hi Kevin,

I am also looking to replace mine with solenoid or proportional valves.
Did=
you have any kind of hysterisis in your control loop? Wouldn't adjusting t=
his have taken out the oscillations?

Regards
Dave...
-----Original Message-----
From: Kevin Hawkins [mailto:lists@xxxxxxx]
Sent: 07 April 2003 01:17
To: ukha_d@xxxxxxx
Subject: RE: [ukha_d] Solenoid Radiator valves


You should also consider using a proportional valve rather than just ON/O=
FF.
I have some ON/OFF ones and I still get oscillation around the setpoint d=
ue
to retained heat (forgotten the tech word) within the radiators. (I was
basically using zone valves)

I have researched a few inline / TVR replacement options =96 You can get
plain ON/OFF down to about =A325 but proportional all seem to be circa =
=A360
plus. There is a very low cost device (TVR replacement) that works on
thermal expansion =96 basically you apply voltage and it heats and expand=
s but
the response time is quite slow.

Kevin


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